Introduction

The allure of buttock beauty has persisted throughout human history, distinguishing us from other mammals and primates due to the distinct presence of this anatomical feature at the base of the spine. Beyond its physiological role, the buttock holds a central position in the definition of bodily beauty. Sexologist Alfred Kind highlights its aesthetic significance, suggesting that the buttocks have historically served as a primary site for presentation and sexual proposition among primates [1, 2].

The evolution of standards for bodily beauty can be traced from historical paintings, such as Raphael’s “The Three Graces” (1503/4), to contemporary times. This transition underscores the dynamic nature of anthropometry in defining beauty. Where a fuller figure was historically deemed beautiful, today’s standards favor a slimmer and more athletic physique. Notably, a well-defined body contour, particularly in the buttock region, is now considered a hallmark of attractiveness.

Reflecting this cultural shift, global trends, as indicated by the ISAPS study [3], reveal a substantial increase in buttock lifts and augmentation procedures, rising by 45.7% and 40.5%, respectively, since 2017. The buttock has become a focal point of bodily beauty, with patients paying meticulous attention to both its shape and volume.

However, the significance of the buttock extends beyond cultural preferences. Positioned between the trunk and lower limbs, it possesses unique anthropometric characteristics crucial for plastic surgery interventions, especially those involving the infiltration of hyaluronic acid (HA). Unlike historical ideals, the contemporary approach to buttock augmentation demands a nuanced understanding of gluteal anthropometry.

This study endeavors to unravel the intricate interplay between gluteal anthropometry and HA infiltration, presenting an all-encompassing protocol designed to optimize the use of HA in gluteal remodeling. Recognizing that neglecting these anthropometric nuances may lead to unnatural aesthetic outcomes, the study advocates for a refined, evidence-based approach to buttock augmentation [4].

Material and methods

Between January 2017 and January 2023, a retrospective study of all patients undergoing HA injections (Genefill Contour Plus, BioScience, 19073 Dümmer, Germany) to improve gluteal contour following a anthropometrically guided HA injection protocol was conducted.The method begins by distinguishing between female and male protocols based on anatomical nuances. For females, specific areas like supragluteal fossettes and lateral buttock are avoided, and caution is exercised in altering the upper V-shaped crease. Central buttock injection is prioritized for gluteal projection, steering clear of the infragluteal fold (Fig. 1). In males, preservation of the lateral gluteal depression is key; projection cannot be excessive as men have a flat sphericity if compared to the woman (Fig. 2).

Fig. 1
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Central buttock injection is prioritized for gluteal projection, steering clear of the infragluteal fold

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Fig. 2
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Male preservation of the lateral gluteal depression

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Anthropometric characteristics are evaluated, favoring thin patients with minimal skin flaccidity. Ultrasonography confirms the absence of contraindications. Exclusion criteria include skin diseases, severe allergies, and other medical conditions [5, 6]. Three steps can be described in gluteal HA treatment: filling smaill depressions on the buttock, addressing depressions in lateral buttocks areas and enhancing central gluteal projection for increased volume.

Specific measurements, including SRI-SLI, RGT-LGT, and intergluteal sulcus, are utilized. An oval is drawn for precise volume augmentation while avoiding specific areas to maintain natural anthropometry (Fig. 3a, b). Five phases can be described in our injection protocol.

Fig. 3
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An oval is drawn for precise volume augmentation while avoiding specific areas to maintain natural anthropometry

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Phase I—preoperative markings

  • Patient markings in an upright position for accurate evaluation

  • Identification of the targeted defect or treatment area

Phase II—asepsis and anesthetic infiltration

  • Asepsis with antiseptic soap and chlorhexidine

  • Infiltration of 10 cc Carbocaine 2% (mepivacaine hydrochloride injection, Pfizer, Lake Forest, USA) at only one entry point for each buttock in case of only volume projection, located 3 cm above the area of influence of HA (Fig. 4a)

Fig. 4
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Infiltration of 10 cc Carbocaine 2% at only one entry point for each buttock in case of only volume projection

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Phase III—HA injection

  • Employing an 18-gauge needle cannula for injection (Fig. 4b)

  • Injection immediately above the fascia of the gluteus maximus muscle, during the procedure, ultrasound-guided infiltration for depth assurance (Fig. 5)

  • HA volume variation (30–50 ml) based on desired outcomes. Then, we draw an oval that has a wide lower base that corresponds with the line that joins the two large trochanters; above it is 3 cm from the SRI-SLI line; medially, it is 2 cm from the inter gluteal sulcus; 3 cm laterally from the great trochanters (Fig. 4c)

  • The gluteal projection reaches up to an increase of 1.5 cm when at least 60 cc of HA is inserted per side (Fig. 6)

Fig. 5
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Injection immediately above the fascia of the gluteus maximus muscle, during the procedure, ultrasound-guided infiltration for depth assurance

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Fig. 6
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The gluteal projection reaches up to an increase of 1.5 cm when at least 60 cc of HA is inserted per side

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Phase IV—final massage for even distribution

  • Vigorous massage to ensure uniform HA distribution (Fig. 4d)

Phase V—post-injection evaluation

  • Assessment of patient and physician satisfaction using aesthetic improvement ratings

  • Pain evaluation on a scale of 1 to 10

Results

A total of 60 participants, with 55 (91.6%) females and 5 (8.4%) males, were enrolled in the study, reflecting a diverse demographic with a mean age of 35.5 years (range, 21 to 53). The injection volume varied, averaging 60.6 ± 39.4 ml per subject (range, 15 to 100 ml).

Participants reported an average pain score of 4.8 ± 2.6 (range, 2 to 8), with no apparent correlation between pain and injection volume, indicating pain independence from gel volume.

Early side effects were observed in every fourth subject (n = 7), primarily reporting pain (n = 6). Other side effects included one case of ecchymosis, with no complaints of rash, induration, or other complications. Incidence rates for any side effect, severe pain, and ecchymosis were 0.21, 0.18, and 0.03, respectively.

All 60 patients completed follow-ups at 7 to 14 days and 3 to 6 months. The average investigation period for the 7 to 14 days assessment was 10.0 ± 4.5 days, while for the 3 to 6 months assessment, it was 118 ± 29 days.

Aesthetic improvement ratings (“very good” and “good”) by both patients and physicians were notably high at 7 to 14 days (94%) and remained consistent at 3 to 6 months (100%). Representative cases illustrating improvements in gluteal contour were documented.

No delayed side effects or complications were reported, and none of the subjects required additional treatments such as corticosteroids, antibiotics, or hyaluronidase. Long-term satisfaction remained high, with no significant changes noted until the 3 to 6 months investigation.

Representative cases

Six representative cases demonstrated the efficacy and safety of HA injections for gluteal contour enhancement, aligning with Meyer’s properties studied in the 1970s. These results underscore the positive aesthetic outcomes and safety profile of HA injections for gluteal contour improvement, supporting the viability of this intervention in clinical practice.

  • Case 1: cellulitis treatment (female, 40 years old, 7 days Post Op. Back view Total amount of infiltration 10 ml Genefill Contour Plus)

  • Case 2: depression generated by a liposuction (female, 28 years old, immediately Post Op. Back view Total amount of infiltration 30 ml Genefill Contour Plus)

  • Case 3: lateral depression treatment (female, 32 years old, immediately Post Op. Back view Total amount of infiltration 50 ml Genefill Contour Plus)

  • Case 4: lateral depression treatment (female, 38 years old, immediately Post Op. Back view Total amount of infiltration 60 ml Genefill Contour Plus)

  • Case 5: lateral depression treatment and central projection (female, 41 years old, immediately Post Op. Back view Total amount of infiltration 60 ml Genefill Contour Plus)

  • Case 6: lateral depression (female, 42 years old, immediately Post Op. Total amount of infiltration 70 ml Genefill Contour Plus)

Discussion

The profound molecular dynamics of HA, a key constituent of human connective tissue, have laid the foundation for its transformative role in aesthetic medicine. Discovered in 1934 by Karl Meyer and extensively studied in the 1970s, HA’s unique structure, characterized by a non-sulfured glycosaminoglycan without a protein core, allows it to form a reticular structure [7, 8]. This structure serves as a molecular scaffold, crucial for maintaining tissue shape and tone [8] The evolution from permanent body fillers to transiently permanent HA signifies a paradigm shift, introducing a level of flexibility that aligns with the dynamic nature of aesthetic practices [9, 10].

The study navigates through the landscape of gluteal augmentation, emphasizing the drawbacks of traditional methods involving silicon gel prosthesis or fat transfer [11,12,13]. These methods, confined to operating rooms, present increased patient involvement and recovery times. In contrast, the study champions non-invasive gluteal augmentation using HA, reflecting the broader trend in favor of minimally invasive procedures due to quick recovery and easy pain management.

Central to the study is the formulation of a specialized protocol for gluteal augmentation using HA, guided by meticulous anthropometric measures. Recognizing the inherent differences between male and female buttock anatomy, the study underscores the importance of respecting gluteal anthropometry. This tailored approach ensures optimal aesthetic results while mitigating complications, reflecting a nuanced understanding of the intricacies involved in gluteal modeling.

The discussion sheds light on the patient-oriented approach, emphasizing the growing preference for non-invasive treatments. Factors such as minimal invasiveness, predictable results, and the use of natural materials contribute to the increasing acceptance of procedures like HA infiltration for gluteal remodeling. The study aligns with this patient orientation, positioning HA as a viable and patient-friendly option. There is research from 2018, aside American Society of Plastic surgery, this study shows that in 2000 the number of aesthetic medicine procedures was 4,847,561, while in 2018, they were 15,909,931; based on this report, the increase in non-invasive procedures increased by 228% (Fig. 7).

Fig. 7
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The increase in non-invasive procedures

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In addressing the potential risks associated with HA infiltration, the discussion provides essential risk mitigation strategies. Emphasizing the importance of slow infiltration and the use of a single entry access point with large cannulas, the study aims to minimize the risk of HA emboli [14]. These strategies not only prioritize patient safety but also contribute to the overall success and acceptance of the procedure.

The study transparently acknowledges its limitations, including its retrospective nature and the need for larger comparative or prospective studies. Recognizing the importance of patient selection, particularly in cases of excessive gluteal skin flaccidity, adds a layer of caution to the findings. The discussion calls for future studies with expanded scopes, drawing explicit connections with existing literature and incorporating comparative analyses with alternative fillers.

Conclusions

In our exploration of gluteal augmentation with HA, our injection protocol for gluteal remodeling stands out for its safety and precision, redefining buttock contours with a focus on efficacy and patient satisfaction. Our findings center on judicious HA application, emphasizing volume optimization, avoidance of excess amounts, and adherence to gluteal anthropometry. Concentrating HA on the gluteus maximus muscle fascia, guided by anthropometric calculations, elevates the procedure beyond augmentation to recreate a geometrically perfect shape. Our study highlights the versatility of the HA procedure, effective in modeling and enhancing buttock shape. Its non-invasive nature aligns with the evolving landscape of aesthetic medicine, meeting patient preferences for swift recovery and easier pain management. The presented HA protocol holds promise for future research and clinical practices in gluteal augmentation. A nuanced approach, considering anthropometric factors and patient preferences, has the potential to set new standards in buttock improvement. While demonstrating safety and efficacy, our study acknowledges limitations, urging larger sample sizes, comparative analyses, and prospective designs for refined protocols in aesthetic medicine. Achieving optimal gluteal augmentation requires mastery and a deep understanding of anatomy and patient preferences. Our study contributes to this evolving narrative, emphasizing the artistry involved in reshaping contours and enhancing patient satisfaction.